Siyu (wanda kuma ake kira Siâ) yare ne na Austronesian wanda kusan mutane 3,500 ke magana a arewacin gabar tekun Huon Peninsula a Lardin Morobe, Papua New Guinea . A cewar Harding da Clark (1994), masu magana da Sio sun zauna a ƙauye ɗaya a kan wani karamin tsibirin da ke bakin teku har zuwa Yaƙin Pacific, bayan haka suka kafa ƙauyuka huɗu a bakin tekun da ke kusa: Lambutina, Basakalo, Laelo, da Balambu. Nambariwa, wani ƙauyen bakin teku da ke da nisan kilomita zuwa gabas, shi ma yana magana da Siyu
Michael Stolz (ya mutu a shekara ta 1931) na Ofishin Jakadancin Lutheran na Jamus Neuendettelsauer ya isa a shekara ta 1910, kuma mazauna ƙauyen Sio sun tuba a cikin 1919. "Tun daga wannan lokacin Sio sun samar da masu bisharar Lutheran da yawa, ma'aikatan mishan, malamai, da ma'aikatan coci" (Harding da Clark 1994: 31). Koyaya, an sanya ƙauyukan Sio a cikin mafi yawan yankin yaren Papuan Kâte, maimakon mafi yawan yankin Harshen Jabêm na Austronesian. Rubutun Sio na farko ya dogara ne akan na Kâte, kuma an yi amfani da shi a cikin bugawa a 1953 na Miti Kanaŋo, littafi mai dauke da labarun Littafi Mai-Tsarki, Luther's Small Catechism, da kuma waƙoƙi 160, duk a cikin harshen Sio. Stolz shine babban mai fassara, kodayake yawancin waƙoƙin sun hada da masu magana da harshen Sio, kuma L. Wagner, wanda ya gaji Stolz, ya shirya dukkan ƙarar.